Transfer resistor and method of making



G. H. RODGERS, JR

Filed Dec. 20, 1948 ATTORNEY Dec. 1, 1953 TRANSFER RESISTOR AND METHOD OF MAKING R.R. mw M mm m6 0 0 R. H m v. MB 7 C m 4 2 8 9 w 3 4 2 5 a 4 m 4 a 4 u hr 7 H 3 Jim f a MW i??? E! H a a Z a a L 5 P m E 4 Q 0 3 Patented Dec. 1, 1953 TRANSFER RESISTOR AND METHOD- OF MAKING George H. Rodgers, Jr., Inglewood, Calif., assignor to North American Aviation, Inc.

Application December 20, 1948, Serial No. 66,386

6 Claims.

This invention pertains to the use of the variable semi-conducting properties of germanium crystals as electrical amplifiers. It particularly pertains to the manufacture of a device which takes advantage of those properties.

Amplifying properties are exhibited by a germanium crystal if it is arranged so that two small electrodes are mounted so as to touch one face of the crystal with a separation of the order of two or three one-thousands of an inch and a third contact is made with the base of the crystal. The amplification is apparent between a potential applied to the crystal between the base of the crystal and one electrode (emitter) and a current flow in a circuit comprising the other electrode (collector) and the base of the crystal. Such an arrangement or device has been denoted a transfer resistor or transistor.

In the past, the fabrication of satisfactory devices of this type has been complicated because two characteristics-spacing of the collector and emitter electrodes, and the pressure exerted by them on the crystalare critical. Therefore,'it has been necessary to employ a large amount of highly skilled labor in their manufacture, and to perform the critical adjustments under the microscope. Furthermore, these precision adjustments imposed a lower limit upon the practicable size of the transfer resistor which would otherwise not have been imposed. The germanium crystal itself is normally of the order of 1 6 inch on a side and the collector and emitter electrodes need be no larger than one hundredth of an inch in diameter. Yet because of the method of fabrication heretofore used, it has been impracticable to attain the small size indicated by the above dimensions.

A further diificulty has been that the hand adjustment factor in each individual transfer resistor has prevented the attainment of unicharacteristics than the others.

It is therefore an object of this invention to It is a, further object of this invention to provide a transfer resistor with fixed spacing between emitter and collector electrodes and with easily adjustable pressure by emitter and collector electrodes on the germanium crystal.

It is still afurther object of this invention to provide a method and means for making transfer resistors of minimum size with a minimum of microscopic adjustment and skilled labor.

Other objects of invention will become apparent'from the following description taken in connection with the accompanying drawings, in which Fig. 1 is a view of a transfer resistor constructed according to this invention;

Fig. 2 is an enlarged partial view of a component of the device shown in Fig. l;

Fig. 3 is a view of amodified form of the invention;

Fig. 4 is an enlarged partial view of a component of the device shown in Fig. 3;

Fig. 5 is a view of a second modification of the invention;

Fig. 6 is an enlarged detail view of a part of the device shown in Fig. 5; and

Fig. 7 is a plan view of the equipment used to assemble the device shown in Fig. 5.

, nected at one end to leads 5 and 6 in insulating block I, and at the opposite end touch germanium crystal 8 held in mount 9 by set screw [0, and spring ll. Mount,9 and insulating block 1 are held in rigid relationship by tubular case 25.

Zshows how conductors l and 2, which are the emitter and collector electrodes in the completed device, are fabricated so as to eliminate haphazard spacing and non-uniformity. Conductors I and 2, which may conveniently be of tungsten or Phosphor bronze, are cemented,

molded, or laminated to strips of plastic insulaprovide a transfer resistor which is relatively easy which eliminates tedious precision adjustments,

, electrode.

tion which form insulators 3 and i to separate and cover, respectively, the assembled electrode. This operation may be carried on to form indefinitely long continuous lengths of assembled When it is desired to fabricate a transfer resistor, it -is necessary-only to cut a short length of assembled electrode normal to its axis, and bevel the ends of conductors i and E as indicated in Fig. l by grinding the edges, the

grinding being conducted on each side toward the point to leave a burr on the ends of the piec exsep rat l8v 3 tending beyond the insulating material. The opposite end of the piece is uncovered and the two electrodes attached to leads in block I. The end of insulator 3 fits firmly against block 1 where it can be cemented in place. Conductors I and 2 contact the face of germanium crystal 8 and, since ier a e se ara e by i su a r s p. a held rig-idly in s fixes spatial interrelation h p. In order to improve contact between crystal 8 and the electrodes, it may be necessary to electrge plate the ends of conductors l and 2 briefly, thereby extending them a sriiall distance beyon the ends of insulator 3.

.The amount of pressure exerted $129? the crystal by the electrodes is controlled by spring II which is chosen to give the optimum pressure with a given electrode lefigtli and spacing be tween top and bottom of the transfer resistor,- Since these factors can be kept constant using th method ei iesr ee iea t Problem iu tine sr eeere is. ie etieiell elim na d- Se scr w i is pro ide temske the elation hip between cry tal and. electrod s r id,

Fig. e snews somewhsi m dif ed rm of. th nventien. wh ch the el ct odes a e refined y platin a. cont nu u stri oi me al 11 a lastic or eereieie od E e trodes 1.2 and ed. b e ee i e et ne, enw tr 14. sc atchin a. slee e through t e deposits; 'e' ierml'i o eubl antifi qua sides of met h ormati n of. his eme t oi. th transfer resistor can be continuous" and of indefinit ly e le t s Whenin t an er sister nered, the appr ciate length s cu en b v edfss shown. Pi. 4 ii. a l ne normal to the plane of the pl" ed material, and the p mater al is eve d Sli t y o. b ing e metallic points in contact with the germanium c sta Th s me re ult may be. achieved by brief electroplating as indicated reference to E sn Figs. 5 and 6 Show a third embodiment of the nvention T Phosphor bron e wi e (5. a r6, cos-.02 of inch in d ameter, boomer bly -1.Q. of. an are, n e in" a iimi us snare-s y a t eii 1 fhew l te. eei e led. firmly to he epar to 6, i e a ooiiiimie isessemii y. wh hi .d wi l he eite' be 'enei it name tw .uii ie niiy separate Q iess er b on e w e e ns. the ier resis or Th g d tub ma b o ee em ma r el. a d th sepsta r. mine. of. Les i A1t i'ti et ve e t be;

iif i k enci e e tr be oug t together continuously by shame-ling two Eho'sphor bronze wires continuously, drying them, and bringing them, together with only the thickness of the enamel separating them, and covering them by extruding ther'nin a plastic eeetine ma e l. 11 as e wr e e fied; nelxsty e e ele e r sin, to orm a rigid integral shell. For the assembled transfer resist r shown in Fig. 5, pencil is is held mach j ustable position in case 25 ofthe transfer tosistor. A set screw 21' is' provided to fix the pencil at optimum pressure against germanium crystal 22 supported on base 23 by spring 24 bearing against screw 34. Crystal 22 is attached to base 23 to make adjustment more convenientwith screw 34. I

To construct this embodiment of; the invention the continuously formed pencil is sharpened by insertionin a rigid holding blockarid by'turn- ,28, and 29.

ing and grinding it at an angle against a grinding wheel. The pencil is then cut in appropriate lengths normal to its longitudinal axis. The ends of the electrodes which are to contact the crystal may be slightly extended by electrolytic deposition upon them of platinum in potassium hydroxide to assure firmer contact with the crystal, i iiit no1finally this is not necessary because grinding of the pencil point produces microscopic burrs which extend beyond the plastic or enamel insulating material. The pencil is then inserted into case 25 by means of the arfangement shown in Fig. 7. A flat plate of insulating material mounts terminal posts 28 and 29 attached to resistance meters 30 and 3|. Re-

sistance meters 30 and 3| are also attached to metal clamp 32 which contacts the base of the germanium crystal either through case or metal backplate 33. The unsharpened end of the pencil is stripped, exposing the bare Phosphor br ze wires. These separated as shown in '7 and the point of the pencil is placed in the open end of the case 25 with the two stripped ends of Phosphor bronze wire against terminals case 25 is slowly brought up under clamp 32 until meters and 3| read an equal fifi lififi, indicating equal pressure of the electrodes oil the germanium Crystal. set screw 2| is then tightened to secure the relationship. A small drop or cement may be applied to pencil l9 and case 25 to further secure their rigid relationship. Set screw 34 in the opposite end of case 25 is then tightened until the optimum readings of meters 30 and 3| are secured. An additional drop or cement may be appued to set screw 34 to prevent accidental displacement from adjusted position. The entire assembly may then be dipped in plastic material, such as a1ow=shrinkageoasimg resin, to seal and secure the entire assembly.

There are thus provided transfer resistors and methods or making them which assure uniformity ofroduct, ease or construction, simplicity, and versatility in size. Since the steps involved are principally mechanical, the transferresistor may be made very small, being limited only by the minimum crystal and conductor sizes which, as pointed out he'ril-ibfore, are not serious limitations.

Although the invention has been described and illustrated in detail, itis to be clearly understood that the same is by way of illustration and example ohiy and is not to be taken by wayof limitation, the spirit and scope of this invention being limited orilyby the terms of the appended claims.-

Iclaim:

l. A double electrode for germanium alloy crystal transfer resistor devices comprising two parallel conductors having uniform oross=sectional areas of .000005- to .00001 square inch, means for separating said conductors by from .001 tov .005: inch and means for holding the aforesaid means inrigid assembly.

2.. The method or making electrodes for a germanium alloy crystal transferresistor comprising securing two similar electrical conductorsto a binding and' insulating strip of constant thickness and indefinite length to; form a continuous double electrode, cutting said double electrode normal so its longitudinal axis into predetermined lengthsxarid. extending said. electrical conductors. by electrolytic deposition.

3- he e h d; Q fi kifi uniiormm spaced collector and emitter electrodes for a transfer 5 resistor comprising rigidly attaching in parallel orientation and at predetermined distance apart two metallic conductors to a continuous insulating strip of indefinite length, cutting the resulting continuous assembly into predetermined lengths and extending said metallic conductors by the electrolytic deposition of metal on the cut ends of said conductor to thereby obtain collector and emitter electrodes.

4. The steps in making a transfer resistor comprising continuously applying a uniform film of enamel to two Phosphor bronze conductors of indefinite length, drying said enamel, and applying a plastic casting material to said conductors while parallel and adjacent to each other to thereby form a double electrode capable of reproduction with uniform internal spacing between conductors.

5. Electrical amplifying means comprising a crystal exhibiting semi-conductive properties, a tubular holder for said crystal adapted to allow freedom for translational motion of said crystal in one direction only, means for adjusting the position of said crystal in said holder while maintaining resilient pressure on it, a cylindrical member fitted within said holder in opposed position to said crystal containing two conductors adapted to contact said crystal at a predeteropposed position within said holder when said adjustment is completed.

6. A device as recited in claim 1 in which said conductors comprise metallic strips plated as a single metallic strip on an insulating strip and in which said means for separating said conductors is a scratch inscribed on said single metallic strip to thereby divide it into separate conductors.

GEORGE H. RODGERS, JR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 756,676 Midgley Apr. 5, 1904 817,664 Plecher Apr. 10, 1906 2,156,660 Van Geel May 2, 1939 2,402,839 Oh] June 25, 1946 2,432,116 McLean et al. Dec. 9, 1947 2,476,323 Rack July 19, 1949 2,486,776 Barney Nov. 1, 1949 2,524,033 Bardeen Oct. 3, 1950 2,524,035 Bardeen et al. Oct. 3, 1950 2,572,993 Douglas et a1 Oct. 30, 1951 2,583,008 Olsen Jan. 22, 1952 2,615,965 Amico Oct. 28, 1952 

